Air tanks must be drained regularly and the discharge observed for abnormalities. Some moisture may be discharged from the supply tank. A much smaller amount of moisture may be discharged from the remaining air tanks. A significant quantity of moisture being discharged from the supply tank — even when the tank is drained on a regular basis — may be normal. Discharge of a significant quantity of moisture from the remaining air tanks is not normal and should be reported.
While a small amount of oil may be found in the supply tank, any visible quantity of oil should be reported or repaired. When oil is found in any other air tank, there is risk of air brake system contamination and the condition must be reported.
When there is a sudden increase in the amount of moisture or oil drained from any tank, the condition must be reported and repaired. Any malfunctioning drain valve must be repaired.
The supply tank should always be drained first to prevent accumulated moisture in the supply tank passing further into the system. Drivers must know the location of all air tanks and drains.
It is important to note that the body design and suspension of some vehicles may limit safe access to the air tanks and drains unless the vehicle is supported on a hoist, or is over a pit or ramp.
- Ensure that the air brake system is within its normal operating pressure range.
- Locate and drain the supply tank until the valve discharges only clean air.
- Locate and drain the remaining air tanks.
- Watch the discharge from each air tank and ensure that all air tank drain valves function properly.
The vehicle passes the test when each drain valve functions properly.
The vehicle fails the test when any drain valve fails to function properly.
Important: The Ontario Highway Traffic Act and regulations prohibit the operation of a vehicle with defective air tank drain valves.